The present invention relates to a distance information obtaining device for determining a distance between a camera or similar image pickup device and an object for each pixel of the image pickup device.
A range finder capable of determining a distance between an image pickup device such as a television (TV) camera and an object on a pixel basis is disclosed in U.S. Pat. No. 4,864,395 issued to the same inventor as the present invention.
In the range finder taught in the above U.S. Patent, a diffraction grating diffracts a white light beam for illumination in a spectral distribution which ranges from red to bluish purple (or violet) and then projects the resulted illuminating beam onto an object. A component of the illuminating beam having a wavelength .lambda. is incident to a point P (located at an angular distance .beta. from the Z axis) on the surface of an object forming an angle .theta. with the normal of the grating (i.e., angle .alpha. as measured from the Z axis). A reflected light beam reflected from the object is propagated through a lens built in the camera to reach a half-mirror. The half-mirror splits the reflected light beam into two beams and causes each of them to follow a different optical path. Each of the two beams is incident to one of two sensors each having a particular spectral sensitivity and sensed at a position on the sensor. The outputs of the sensors each representative of an optical image of the object are fed to a processing unit to produce distance information.
The processing unit calculates the coordinates of the point P by using the coordinates of the center of the grating and the above-mentioned angles .alpha. and .beta.. The angle .beta. is obtained on the basis of the position of the optical image reflected from the point P on the sensor. To determine the angle .alpha., the processing unit determines the wavelength .lambda. of the light beam incident to and reflected from the point P and then the angle .theta. between the light beam of the wavelength .lambda. and the normal of the grating. Further, the wavelength .lambda. can be calculated on the basis of the ratio R between the outputs of the pixels of the two sensors to which the reflected light beam from the point P is incident. To determine the ratio R accurately, it is necessary for the sum of the outputs of the two sensors to be sufficiently great.
The conventional range finder stated above uses two sensors each having a particular spectral sensitivity, and illuminates each point of the object with the light beam having various wavelength components. The problem is, therefore, that the outputs of both sensors may be lowered and, therefore, the accuracy of the ratio R between the outputs is degraded, depending on the wavelength of the reflected beam, i.e., the point of the object to be measured.
Such a problem is also derived from the difference in the color of an object. Specifically, since the spectral intensity of the reflected light beam is modulated by the reflectance of the object, the ratio R, which is obtained by the reflected beam at a point illuminated by a component of the beam having a wavelength of low reflectance, is not accurate, degrading the accuracy of measurement.